A telecommunication system which will be discussed in the present patent application is a system comprising a number of telecommunication modules responsible, say, for a plurality of telecommunication channels and connectable to a main unit which supplies the modules with power, deals with data traffic from/to the modules and performs control of the modules. A MUX-DMUX block may serve an example of such a main unit interconnected with a number of telecommunication modules serving respective optical channels.
One of the problems, known to specialists in the field for such systems, stems from sharp fluctuations of voltage/current when trying to insert a module to the system, especially when the modules consume currents relatively greater than the current consumed in the main block. Since the power fluctuations may lead to damages both in the main unit and in the modules and, of course, to errors and numerous alarms in the data traffic, the modules are normally exchanged off-line. The off-line operations usually require shut-down of a card carrying the main unit for a period of time while a trained technician performs any desired changes in the system's configuration.
As has been mentioned, the changing power supply voltage may damage the modules. For example, when connecting a module to the main card, the power voltage applied to a particular element at its power contact grows slowly and, at the beginning of the connection process occurs to be lower than a control signal if already applied to the element's control gate. For preventing damage of such elements of the module, the following known solution is widely used. The modules to be interconnected with the main card are usually provided with longer pins of the power supply contacts so that, in the process of installing, they are brought into contact with the main unit power supply earlier than any other contacts of the module get into connection with their respective matches. Thus, when the module is completely connected to the main unit, the power supply voltage in the module might already be stable.
U.S. Pat. No. 5,371,743 describes the above “long pins” solution and a method of providing on-line replacement of a module which is at a specified position in an array of modules connected to a common control processor via a common voltage bus. When the module is removed, an indication is provided to the control processor showing that a removal has occurred and identifying the position thereof. When the replacement has occurred, an indication thereof is provided to the control processor. The US patent describes a system where the modules communicate with the control processor via common interface buses; the processor in such case enables that the modules are never connected to it together and therefore no module, during a transition process which may occur between it and the central processor, affects traffic in adjacent modules. The system described in the U.S. patent cannot be used for optical equipment.
U.S. Pat. No. 5,862,350 describes a similar “long pins” solution, but for asserting a busy line of SCSI bus being connectable to a number of devices. More particularly, it is a mechanism and a method for quiescing a SCSI bus by asserting the busy signal just prior to the SCSI signal pins making contact or decoupling during a hot modification. A hot modification is an insertion, removal or exchange of a device coupled to a SCSI interface bus while the system is operating (e.g., not powered down). By asserting the busy line for a predetermined and short period of time during the disturbance of the SCSI signal pins, glitches or noise introduced by the coupling or decoupling of the signal lines is isolated and prevented from causing transmission errors over the SCSI bus. According to the system described, any communication over the SCSI bus made just prior to the hot modification is allowed to complete before the signal pins are interrupted. For hot insertions, the system utilizes longer pins on the connector to assert the busy line just before coupling of the other pins of the connector. For removal, a special pair of short pins are placed on the connector to assert busy when decoupled. In either case, the busy line is then maintained as asserted for a predetermined period of time after the initial assertion to allow for communication over the SCSI bus to terminate before the hot modification.
None of the prior art references gives a simple practical solution for hot insertion of multiple modules in optical telecommunication networks.
At present, no live insertion of optical communication modules is ensured in the known equipment of telecommunication networks, and all repairs or reconfiguring operations are provided off-line.